The commercially available lubricant compositions are produced from a multitude of different natural or synthetic components. The lubricant compositions comprise base oils and further additives. The base oils often consist of mineral oils, highly refined mineral oils, alkylated mineral oils, poly-alpha-olefins (PAOs), polyalkylene glycols, phosphate esters, silicone oils, diesters and esters of polyhydric alcohols.
Currently Group II and Group III hydrorefined paraffinic mineral oil, GTL synthetic oil and poly-α-olefin are preferably used as base oil in lubricant compositions. However, these base oils have a detrimental effect on sealing materials which form a part of engines and mechanical transmission units. In particular, the use of these base oils leads to the shrinkage of sealing materials such as acrylonitrile butadiene rubber.
It is known that polyesters, however, accelerate the expansion of these sealing materials. Thus, specific polyesters are used in lubricant compositions in order to counteract the shrinking effect of modern base oils. In particular DIDA (diisodecyl adipate), DITA (diisotridecyl adipate) and TMTC (trimethylolpropane ester with decylic acid) are used to achieve this purpose.
In addition, the viscosity index is an important characteristic of polyesters when used as a fluid in a lubricant composition. A high viscosity index signifies that the temperature dependence of the fluid is small. Thus, a fluid which has a high viscosity index will have a low viscosity at low temperature and can be used to reduce the power consumption of an engine on start-up. In general, fluids with a high viscosity index have been shown to be more energy efficient. Thus, there is still a need in the industry to obtain fluids such as synthetic oils with a high viscosity index in order to enable energy conservation by using lubricant compositions containing those fluids.
Another advantageous characteristic of lubricant formulations is improved low temperature behaviour as expressed by low cloud points. The cloud point of a fluid such as a lubricant formulation is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance.
U.S. Pat. No. 4,623,748 describes polyesters obtainable by reacting adipic acid and aliphatic alcohols such as nonanol. These polyesters can be used as lubricants.